Method for manufacturing iron silicide nano-wires

ABSTRACT

A method for making iron silicide nano-wires comprises the following steps. Firstly, providing a growing substrate and a growing device, the growing device comprising a heating apparatus and a reacting room. Secondly, placing the growing substrate and a quantity of iron powder into the reacting room. Thirdly, introducing a silicon-containing gas into the reacting room. Finally, heating the reacting room to a temperature of 600-1200° C.

BACKGROUND

1. Technical Field

The present invention relates to methods for making nano materials and, particularly, to a method for making an iron silicide (FeSi) nano-wires.

2. Discussion of Related Art

Iron silicide (FeSi) is a narrow-bandgap semiconductor with a cubic structure, which can be applied in the field of Spintronics (Spin Electronics) due to its unusual magnetic behavior. Therefore, achieving various iron silicide (FeSi) nano-wires is desirable.

A conventional method of making iron silicide (FeSi) nano-wires according to prior art includes the following steps. Firstly, providing a silicon substrate, a quantity of anhydrous FeCl₃ powder (boiling point 319° C.) and an alumina boat. Secondly, placing the silicon substrate and anhydrous FeCl₃ powder separately in the alumina boat, and then placing the alumina boat into a horizontal-tube furnace. The FeCl₃ powder is placed between the gas inlet of the horizontal-tube furnace and the silicon substrate. Thirdly, introducing a N₂ gas into the horizontal-tube furnace. Finally, heating the horizontal-tube furnace to a temperature of 1100° C. The FeCl₃ powder is vaporized when the temperature is above 319° C. The vapor-phase FeCl₃ was carried by the N₂to reach the silicon substrate and react with the silicon from the substrate to grow iron silicide nano-wires. The iron silicide nano-wires is along the [111] direction and distributed disorderly on the surface of the silicon substrate.

However, there are some drawbacks in using this method. Firstly, high temperature is needed, usually above 1100° C., to grow iron silicide nano-wires, which consumes a lot of energy and is costly. Secondly, silicon substrates are required to grow the iron silicide nano wires.

What is needed, therefore, is a method for making iron silicide nano-wires at low temperature on a low cost substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present method for making the iron silicide nano-wires can be better understood with references to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present method for making the iron silicide nano-wires.

FIG. 1 is a flow chart of a method for making an iron silicide nano-wires, in accordance with a present embodiment.

FIG. 2 is a schematic view of a growing device used for making the iron silicide nano-wires of FIG. 1.

FIG. 3 is a Scanning Electron Microscope (SEM) image of the iron silicide nano-wire clusters formed by the method of FIG. 1.

FIG. 4 is a Scanning Electron Microscope (SEM) image of the iron silicide nano-wires formed by the method of FIG. 1.

FIG. 5 is a Transmission Electron Microscope (TEM) image of the iron silicide nano-wires formed by the method of FIG. 1.

FIG. 6 is an X-Ray Diffraction (XRD) result of the iron silicide nano-wires formed by the method of FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the present method for making the iron silicide nano-wires, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION

References will now be made to the drawings to describe, in detail, various embodiments of the present method for making an iron silicide nano-wires.

Referring to FIGS. 1 and 2, a method for making the iron silicide nano-wires includes the following steps: (a) providing a growing substrate 312 and a growing device 30 that includes a heating apparatus 302 and a reacting room 304; (b) placing the growing substrate 312 and a quantity of iron material 314 into the reacting room 304; (c) introducing an silicon-containing gas into the reacting room 304; and (d) heating the reacting room to a temperature of 600˜1200° C.

In step (a), the reacting room 304 can be a quartz tube with a gas inlet 306 at one end and a gas outlet 308 at an opposite end. The quartz tube is movably located in the heating apparatus 302. The length of the quartz tube is more than the length of the heating apparatus 302 so that part of the tube can be used a handle when moving it while still keeping a substantial part of it heated in the heating apparatus 302.

Moreover, a carrier 310 with a high melting point can be disposed in the reacting room 304. In the present embodiment, the carrier 310 is a ceramic boat. The shape of ceramic boat is arbitrary and the volume thereof can be selected according to need.

In step (a), the growing substrate 312 used is made from a non-metallic material with high melting point (e.g. silicon, silicon dioxide, quartz, glass, sapphire, etc). In the present embodiment, the growing substrate 312 is a silicon wafer. The size of the silicon wafer is arbitrary and can be selected according to need. The growing substrate 312 is cleaned by ultrasonic vibration before being placed into the reacting room 304. The period of time for cleaning the growing substrate 312 ranges from approximately 10 to 30 minutes.

In step (b), the iron material 314 can be a block or in powder form. In the present embodiment, the iron material 314 is iron powder. Before placing the iron material 314 into the reacting room 304, the iron material 314 is treated by a diluted acid solution for a period of time (e.g. from about 2 to 10 minutes) to remove iron oxide layer present and other impurities on the surface of the iron material 314. In the present embodiment, the diluted acid solution is diluted hydrochloric acid solution. A layer of iron chloride will formed on the surface of the iron material 314 after dipping in the diluted hydrochloric acid. The layer of iron chloride is easy to be vaporized so that the surface activity of the iron material 314 is increased.

The iron material 314 is placed in the carrier 310 to form a layer, and a thickness of the layer ranges approximately from 1 micrometer to 3 millimeters. The purity of the iron material 314 is more than 99.9%.

In step (b), the growing substrate 312 may be placed anywhere in the reacting room 304 as long as one surface of the growing substrate 312 can be exposed to the silicon-containing gas introduced in the following step (c). The growing substrate 312 can be placed above the carrier 310 or anywhere between the carrier 310 and the gas outlet 308. In other embodiments, the growing substrate 312 and the iron material 314 can both be placed in the carrier 310 but not contacting each other. In the present embodiment, the growing substrate 312 is placed directly above the carrier 310.

Before step (c), an optional step (e) of introducing a protective gas into the reacting room 304 could be carried out. The protective gas is used to evacuate the air in the reacting room 304. In the step (e), the protective gas form a gas flow direction 318 from the gas inlet 306 to the gas outlet 308. The flow rate of the protective gas ranges approximately from 200 to 2000 milliliter per minute. The protective gas is selected from a group comprising nitrogen (N₂) gas and noble gases. In the present embodiment, the protective gas is argon (Ar) gas.

Before step (c) and after step (e), an optional step (f) of introducing a hydrogen gas into the reacting room 304 and heating the reacting room 304 to a temperature of 600˜800° C. can be carried out. The protective gas is still added during the introduction of the hydrogen gas. The air pressure in the reacting room 304 ranges approximately from 1 to 15 torrs. The purity of the hydrogen gas is more than 99.99%. The flow rate of the hydrogen gas ranges approximately from 20 to 1000 milliliters per minute. The period of time for introducing the hydrogen gas ranges approximately from 10 to 20 minutes. The hydrogen gas is used to reduce the oxide on the surface of the iron material 314. It is to be understood that the process of introducing the hydrogen gas into the reacting room 304 can be carried out before, during or after heating the reacting room 304.

In step (c), the silicon-containing gas is introduced into the reacting room 304 after the hydrogen gas is introduced for about 10 minutes. The silicon-containing gas is introduced in a manner so that it flows from the iron material 314 to the growing substrate 312. A guide (not shown) can be used to direct the flow direction of the silicon-containing gas in any desired path. The protective gas and hydrogen gas is still added during the introduction of the silicon-containing gas. The air pressure in the reacting room 304 ranges approximately from 1 to 20 torrs. The silicon-containing gas can be selected from the group comprising silicon halide, silane, silane derivative, halogenated silane and combination thereof. The flow rate of the silicon-containing gas ranges approximately from 10 to 1000 milliliters per minute. In the present embodiment, the silicon-containing gas is silicon tetrachloride (SiCl₄) gas and the flow rate of the silicon-containing gas is 100 milliliters per minute.

In step (d), the reacting temperature ranges approximately from 600 to 1200° C. The rate the temperature increases in the reacting room 304 is 20° C. per minute. The period of time for growing the iron silicide nano-wires ranges approximately from 10 to 90 minutes. The vapor-phase Fe reacts with the silicon-containing gas to fabricate iron silicide nano-wires on the growing substrate 312.

In the present embodiment, the iron silicide nano-wires are fabricated at a temperature of 800° C. Referring to FIGS. 3 and 4, the iron silicide nano-wires in the present embodiment are in form of a single nano-wire or in form of nanowire clusters. The iron silicide nano-wires are disorderly distributed on the growing substrate 312. A diameter of the iron silicide nano-wires range approximately from 10 to 500 nanometers. A length of the silicide nano-wires range approximately from 100 nanometers to 100 micrometers. Referring to FIG. 5, the silicide nano-wires are along [110] direction. Referring to FIG. 6, the XRD result show that the iron silicide nano-wires fabricated at a temperature of 800° C. includes Fe₃Si phase and FeSi phase. The iron silicide nano-wires fabricated at a temperature below 1000° C. include Fe₃Si phase and FeSi phase, but the iron silicide nano-wires fabricated at a temperature above 1000° C. includes only FeSi phase. It is because the Fe atom in Fe₃Si is easily diff-used to the surface of the Fe₃Si crystal lattice at temperatures above 1000° C. and reacts with the silicon-containing gas to fabricate iron silicide nano-wires in the FeSi phase.

The present method for making the iron silicide nano-wires has many advantages including the following. Firstly, the iron material can react with the silicon-containing gas at a low temperature, therefore saving energy and reducing costs. Secondly, the method allows fabrication of the iron silicide nano-wires on different growing substrates.

It is to be understood that the above-described embodiments are intended to illustrate, rather than limit, the invention. Variations may be made to the embodiments without departing from the spirit of the invention as claimed. The above-described embodiments illustrate the scope of the invention but do not restrict the scope of the invention.

It is also to be understood that the above description and the claims drawn to a method may include some indication in reference to certain steps. However, the indication used is only to be viewed for identification purposes and not as a suggestion as to an order for the steps. 

1. A method for making iron silicide nano-wires, the method comprising the following steps of: (a) providing a growing substrate and a growing device, and the growing device comprising a heating apparatus and a reacting room; (b) placing the growing substrate and a quantity of iron material into the reacting room; (c) introducing a silicon-containing gas into the reacting room; and (d) heating the reacting room to a temperature of 600˜1200° C.
 2. The method as claimed in claim 1, wherein the growing substrate is selected from a group comprising silicon, silicon dioxide, quartz, glass, and sapphire.
 3. The method as claimed in claim 1, wherein the purity of the iron material is more than 99.9%.
 4. The method as claimed in claim 1, wherein the iron material are treated by diluted acid solution before being placed into the reacting room.
 5. The method as claimed in claim 4, wherein the diluted acid solution is diluted hydrochloric acid solution.
 6. The method as claimed in claim 1, wherein the iron material situated in form of a layer, and a thickness of the layer ranges from 1 micrometer to 3 millimeters.
 7. The method as claimed in claim 1, wherein at least part of the growing substrate is located above the iron material.
 8. The method as claimed in claim 1, wherein the reacting room comprises a gas inlet and a gas outlet, and the growing substrate is located in the area in-between the iron material and the gas outlet.
 9. The method as claimed in claim 1, further comprising a step (e); step (e) comprises introducing a protective gas into the reacting room before step (c).
 10. The method as claimed in claim 9, wherein the flow rate of the protective gas ranges from 200 to 2000 milliliter per minute.
 11. The method as claimed in claim 1, wherein in step (c) the air pressure in the reacting room ranges from 1 to 20 torrs.
 12. The method as claimed in claim 1, wherein the silicon-containing gas is selected from the group comprising silicon halide, silane, silane derivative, halogenated silane and combination thereof.
 13. The method as claimed in claim 12, wherein the silicon halide is silicon tetrachloride.
 14. The method as claimed in claim 1, wherein there is a flow of the silicon-containing gas, and the flow rate of the silicon-containing gas ranges from 10 to 1000 milliliters per minute.
 15. The method as claimed in claim 1, wherein the silicon-containing gas is introduced in a manner so that it flows from the iron material to the growing substrate.
 16. The method as claimed in claim 1, wherein the period of time for growing the iron silicide nano-wires ranges from 10 to 90 minutes.
 17. A method for making iron silicide nano-wires, the method comprising the following steps of: providing a growing substrate and a growing device, and the growing device comprising a heating apparatus and a reacting room; placing the growing substrate with a quantity of iron material into the reacting room; introducing a hydrogen gas and a silicon-containing gas into the reacting room; and heating the reacting room to a temperature of 600˜800° C.
 18. The method as claimed in claim 17, wherein the purity of the hydrogen gas is more than 99.99%.
 19. The method as claimed in claim 17, wherein there is a flow of the hydrogen gas, and the flow rate of the hydrogen gas ranges from 20 to 1000 milliliters per minute
 20. The method as claimed in claim 17, wherein the reacting room is heated to a temperature of 800˜1200° C. 